1. Field of the Invention
The present invention relates to a thermally efficient printed circuit board that supports one or more integrated circuit packages.
2. Description of Related Art
Integrated circuits are typically assembled into a package that is soldered to a printed circuit board. There are many types of integrated circuit packages such as pin grid array (PGA), quad flat pack (QFP) and ball grid array (BGA). BGA integrated circuit packages include an integrated circuit that is mounted to a substrate. Located on a top surface of the substrate are a plurality of bond pads that are wire bonded to the integrated circuit. The bond pads are connected to solder pads located on the bottom surface of the substrate by routing traces and a number of vias. The integrated circuit is typically enclosed by a plastic material. Solder balls are attached to the solder pads of the package substrate and then subsequently reflowed to attach the package to a printed circuit board.
Most of the heat generated by the integrated circuit conducts through the substrate and the solder balls, and into the printed circuit board. The heat is typically removed from the circuit board by convective heat transfer. The convective heat transfer rate is increased by enlarging the area from which the heat is removed. It is therefore desirable to have the heat conduct outward from the mounting area of the package. The solder balls are soldered to surface pads of the printed circuit board. The surface pads of the printed circuit board are typically circular shaped pads located on a layer of dielectric material. The dielectric has a relatively low coefficient of the thermal conductivity. Consequently the printed circuit board provides a relatively poor conductive path for the heat generated by the integrated circuit.
Some integrated circuit packages incorporate heat slugs and heat sinks to improve the heat transfer rate from the package and increase the overall thermal efficiency of the assembly. Head slugs and heat sinks can significantly increase the cost of the package. It would be desirable to improve the thermal efficiency of the printed circuit board. It would therefore be desirable to provide a BGA circuit board assembly that is thermally efficient and relatively inexpensive to produce.
The present invention is a thermally efficient printed circuit board for a ball grid array (BGA) integrated circuit package. The printed circuit board includes a first outer conductive plane located on a top surface of a substrate. A portion of the first outer conductive plane is covered with a solder mask. The solder mask has an opening that exposes a portion of the first outer conductive plane.